MathRevolution wrote:

[GMAT math practice question]

When x/y = 1.2, (x^2-y^2)/(x^2+y^2) =?

A. 10/51

B. 11/51

C. 10/61

D. 11/61

E. 11/71

\(\frac{x}{y}=1.2\), square both sides to get \(\frac{x^2}{y^2}=1.44\) -------(1)

subtract \(1\) from both sides of equation (1)

\(\frac{x^2}{y^2}-1=1.44-1\)

or \(\frac{{x^2-y^2}}{y^2}=0.44\)

Now add \(1\) to both sides of equation (1)

\(\frac{x^2}{y^2} + 1=1.44+1\)

or \(\frac{{x^2+y^2}}{y^2}=2.44\)

so \(\frac{x^2-y^2}{x^2+y^2} = \frac{0.44}{2.44} = \frac{11}{61}\)

Option

DHi

BunuelCan you confirm the answer or point out errors in my approach because OA is E i.e 11/71